An extremely thermotolerant, alkaliphilic subtilisin-like protease from hyperthermophilic Bacillus sp. MLA64.

The current work is a report on a new extremely thermostable protease from newly isolated hyperthermophilic Bacillus sp. MLA64. The protease was purified with a 16.5-fold increase in specific activity and 93.5% recovery. The molecular weight of the enzyme was estimated to be 24 kDa. The enzyme was extremely stable and quite active over the temperature range from 40 to 100°C with an optimal temperature at 95°C as well as in a wide range of pH from 6.0 to 12.5, with a superlative at pH 9.5. The enzyme activity was not enhanced in the presence of CaCl(2), indicating that the enzyme is calcium-independent. The enzyme showed high stability towards non-ionic surfactants and anionic surfactant SDS. In addition, the enzyme was relatively stable with respect to oxidizing agents. The protease was inhibited by PMSF but not by TPCK and TLCK, suggesting that it can be a subtilisin-like protease. Moreover, the N-terminal sequencing of the first 20 amino acids of the purified protease showed less homology with other well-known bacterial peptidases. In conclusion, the enzyme can be considered as a novel protease which might be a candidate for industrial processes.